Ys Origin

I get stucked in the part that's a place can only pass by activating the boost and destroy 4 monters (the one that shoot in 4 diferente directions), with Yunica and Hugo you gain an item that let you go free in this area.Second floor, the ground is purple, and each monter stays in one corner of the scenarioWhen i active the boost, it ends before i can destroy all the monsters. Someone can help?

Lower your health to about 10% so boost recovers faster.Boost, attack the first monster, retreat, wait for boost to recover, attack the second monster, wait for boost to recover again, attack the third monster, and so on.